Manholes of the type contemplated herein generally include an underground masonry casing, a manhole cover frame which rests on top of the casing and protrudes through the pavement of the street or the like, and a manhole cover which is supported in the manhole cover frame.
It has become necessary, due to the limited capacity of sewer systems, to separate the sewer system from storm systems. Where the storm systems are joined with the sewer systems, the increase of flow during rainstorms produces a flow beyond the capacity of the sewer system. It is, therefore, one of the objects of the present invention to prevent rain water from entering the sewer system through the manhole cover and casing.
Efforts to achieve this object have been directed primarily to internal seals which can be retrofit into existing sewer systems through the manhole cover. These seals are located between the manhole cover frame and the manhole casing to prevent seepage of rain water through the joint between the frame and the casing. These seals have been effective, however, water seeping through the joint will accumulate within the seal inside of the casing and adversely affect the life of the seal.